High temperature insulated aluminum conductor

ABSTRACT

An aluminum or aluminum alloy metal electrical conductor having a high temperature resistant electrically insulating metal oxide coating layer including at least one non-aluminum metal oxide chemically bonded thereto and methods of making and using same

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application Ser.No. 62/034,358 filed Aug. 7, 2014, and U.S. provisional application Ser.No. 62/034,308 filed Aug. 7, 2014, the disclosures of which are herebyincorporated in their entirety by reference herein.

TECHNICAL FIELD

Various embodiments relate to aluminum and aluminum alloy conductorswith an electrically insulating coating.

BACKGROUND

A conventional electrical conductor such as a magnet wire is typically acopper wire coated with a thin sheath of polymeric insulation that isflexible such that the insulated wire can be wound around a magnet toutilize electricity running through the wire to generate a magneticfield. It is used in the construction of a variety of apparatuses whichchange one form of energy into another or which change power densityusing the magnetic field, examples include transformers, inductors,motors, generators, speakers, hard disk head actuators, electromagnets,and other electric machines and applications which require coils ofwire. Likewise, wires carrying low voltage, such as automobile wiringharnesses and other low voltage electrical and magnetic wire assemblieshave conventionally been made of similar sheathed copper wire.

Although copper has better conductivity than aluminum, the demand foraluminum wire has grown due to its lower cost and lighter unit weight(density) compared to copper wire. It takes only one pound of aluminumto equal the current-carrying capacity of two pounds of copper. Aluminummagnet wire is sometimes used for large transformers and motors, butcompared to copper has various drawbacks including requiring about twicethe cross-sectional area of copper wire to carry the same current, suchthat large windings or those requiring large cross-sectional area mayundesirably increase the size of the device housing the coil; and itwould be desirable to reduce the cross-sectional area of the wires, suchas by reducing the thickness of insulation on the metal wire.

Electrical conductors such as magnet wire and low voltage wire areconventionally covered with an electrically insulating layer, generallycomposed of organic material, such as paper, cotton, silk, fiberglasstape or polyester. More recent conventional samples typically use one tofour layers of polymer film insulation, often of two differentcompositions, to provide an insulating layer. These organic coatedmagnet wires limit the life of the products containing them due tofailure in high temperature operation. For example when a drill or smallmotor is used for extended periods, significant heat is generated.Magnet wire insulating films use (in order of increasing temperaturerange) polyvinyl formal, polyurethane, polyamide, polyester,polyester-polyimide, polyamide-polyimide (or amide-imide), andpolyimide. The general difficulties facing organic coatings are poorperformance of the cured coating with respect to corrosion resistance,chemical resistance and high temperature resistance.

Even the most robust organic films, such as polyimide, are resistant totemperatures of only up to about 240° Celsius (° C.). The insulation ofthicker square or rectangular magnet wire is often augmented by wrappingit with a high-temperature polyimide or fiberglass tape, and completedwindings are often vacuum impregnated with an insulating varnish toimprove insulation strength and long-term reliability of the winding.Glass and polyester/glass insulation, such as NEMA Class C insulation,are rated at temperatures greater than polyimide alone, but requirewinding of filaments around wire and generally include organic materialsuch as polyester fiber, varnish or epoxy. These added steps are laborintensive and still have limited high temperature resistance due to theorganic material present.

Attempts to coat wire with inorganic materials have met with limitedsuccess in the magnet wire applications. Aluminum wire having ananodized coating of aluminum oxide has various drawbacks includingembrittlement and inelasticity of the coating at insulating thicknessesresulting in cracks in the coating, particularly when exposed totemperature cycling. Aluminum oxide also spalls and delaminates atincreased temperatures of about 300° C. to 450° C. Manufacturingprocesses for anodizing aluminum wire also have drawbacks. The sulfuricacid electrolyte used in commercial anodizing has been identified as acarcinogen and thus poses safety and health issues. OSHA limits onsulfuric acid in air are only 1 mg/m³. Anodizing of aluminum is alsorelatively slow, e.g. anodization of aluminum takes approximately 1minute to apply 4 microns of aluminum oxide. This and other limitationsof alumina coated aluminum wire are reflected in the limited, if any,commercial successes of anodized aluminum magnet wire in the industry.Other attempts to use inorganic materials include sheaths around copperwire with an inorganic powder filling a space between the sheath and thewire. These sheathed products are labor intensive to produce, includethe more expensive and heavy copper wire and use thick powder filledspaces which significantly increase the weight and circumference of thewire.

There is an ongoing demand in the aerospace, marine, automotive andequipment industries for a low cost, light weight magnet wirereplacement for copper wired electromagnetic coil assemblies suitablefor use in coiled-wire devices, such as transducers, including actuators(e.g., solenoids, electric motors, loudspeakers); sensors (e.g.,variable differential transducer); transformers (e.g. stepdowntransformers for electronics), as well as electric generators andalternators.

In general, an electromagnetic coil assembly includes at least onemagnet wire, which is wound around a bobbin or similar support structureto produce at least one multi-turn coil. When designed for usage withina solenoid, the electromagnetic coil assembly often includes a singlecoil; while, when utilized within a variable differential transducer ora transformer, the electromagnetic coil assembly typically includes aprimary coil and one or more secondary coils. In conventional, non-hightemperature electromagnetic coil assembly, the insulation is commonlyformed from a plastic or other readily-available organic dielectricmaterial. Organic materials, however, rapidly decompose, become brittle,and ultimately fail when subjected to temperatures exceedingapproximately 260° C.; and are consequently unsuitable for usage withinelectromagnetic coil assemblies that exceed about 250° C. during normalor peak usage. Even at temperatures lower than 260° C., temperaturecycling between ambient temperature and peak use temperature tends toage organic insulation. There is a need for magnet wire capable ofproviding prolonged and reliable operation in high temperatureenvironments characterized by temperatures exceeding 250° C.

Conventional organic-based insulation also has the drawback of poorresistance to “hot spots”, which are points of localized increasedtemperature on a wire assembly. These are commonly found in proximity tooperating engines, manifold and exhaust assemblies and the like, whereunintended and/or intermittent contact between, for example, wiring,wiring harnesses and connections causes melting or decomposition of theinsulation resulting in electrical current passing out of the wire andelectrical short circuiting.

Considering the above, it is desirable to provide embodiments of coatedwire suitable for use where temperatures exceed 250° C., e.g. hot spots,and/or in an electromagnetic coil assembly for usage within coiled-wiredevices (e.g., electric machines, solenoids, variable differentialtransformers, and two position sensors, etc.) suitable for operating inhigh temperature environments characterized by temperatures exceeding260° C. and up to about 640° C. Preferably, embodiments of such anelectromagnet coil assembly would be relatively insensitive to radiationand well-suited for usage within nuclear applications. It is desirableto provide embodiments of a method for manufacture such a hightemperature electromagnetic coil assembly.

SUMMARY

In an embodiment, an aluminum or aluminum alloy metal electricalconductor having a high temperature resistant insulating coating isprovided with an aluminum or aluminum alloy conductor. Deposited on thealuminum or aluminum alloy conductor is an electrically insulating metaloxide coating layer comprising at least one non-aluminum metal oxide.The insulating metal oxide coating layer is chemically bonded to thealuminum or aluminum alloy conductor.

In another embodiment, an electrical conductor is provided with anelectrically conductive core having an outer surface, where the corecomprises aluminum. An electrically insulating coating is chemicallyadhered directly on the outer surface of the core. The coating comprisesat least one non-aluminum metal oxide, and is electrically resistant athigh temperatures.

It is another object of the invention to provide an electrical conductorcomprising: an electrically conductive core having an outer surface, thecore comprising aluminum; and an electrically insulating coatingchemically bonded directly on the outer surface of the core, the coatingcomprising at least one non-aluminum metal oxide, the coating beingelectrically resistant at high temperatures.

It is a another object of the invention to provide an electricalconductor as disclosed herein wherein the electrical conductor maintainsan electrical resistance at ambient temperature after heating to atleast 450° C. It is another object of the invention to provide anelectrical conductor as disclosed herein wherein the electricalconductor maintains an electrical resistance of at least 1 Megaohm atambient temperature after thermal cycling to at least 600° C.

It is another object of the invention to provide an electrical conductoras disclosed herein wherein the core comprises an aluminum alloy. It isanother object of the invention to provide an electrical conductor asdisclosed herein wherein the at least one non-aluminum metal oxidecomprises titanium dioxide and the conductor is an aluminum or aluminumalloy conductor. It is another object of the invention to provide anelectrical conductor as disclosed herein wherein the coating has athickness being in a range of 0.5 to 50 microns.

It is another object of the invention to provide an electrical conductoras disclosed herein wherein the electrically insulating coating has anelectrical resistance at ambient temperature before the electricalconductor is used of 3 to 30 Megaohms. It is another object of theinvention to provide an electrical conductor as disclosed herein whereinthe coating has a resistance of at least 4 Megaohms at ambienttemperature after exposure to a temperature greater than 250° C.,preferably greater than 300° C.

It is another object of the invention to provide an electrical conductoras disclosed herein wherein the coating is the sole electrical insulatorfor the electrical conductor and the coating is electrically insulatingat applied voltages of up to 120 volts and peak voltage of up to about140 volts.

It is another object of the invention to provide an electrical conductoras disclosed herein wherein the electrically insulating coating ishomogenous. It is another object of the invention to provide anelectrical conductor of claim 5 wherein the electrically insulatingcoating further comprises aluminum oxide and has an interface with theouter surface of the core; and wherein aluminum oxide concentration isgreater at the interface with the outer surface of the core anddecreases with increasing distance away from the interface.

It is another object of the invention to provide an electrical conductoras disclosed herein wherein the electrically insulting coating has asurface area of at least 100 times greater than the surface area of thebare core prior to being coated with the electrically insulatingcoating. It is another object of the invention to provide an electricalconductor as disclosed herein wherein the electrically insulatingcoating is an electro-ceramic coating.

It is another object of the invention to provide an electrical conductoras disclosed herein further comprising an electrically insulating shellsurrounding the coating, such that the coating is positioned between theshell and the core. It is another object of the invention to provide anelectrical conductor as disclosed herein wherein the electricallyinsulating shell comprises an enamel, a sealant, an organic coating.

It is another object of the invention to provide a wire harness fortransmitting at least one of signals and electrical power, the wireharness comprising at least one wire formed from an electrical conductoras disclosed herein. It is another object of the invention to provide awire harness as disclosed herein, wherein the at least one wire formedfrom the electrical conductor is part of a 120 volts or less circuit.

It is another object of the invention to provide an electric machinecomprising: a winding comprising an electrical conductor as disclosedherein. It is a further object of the invention to provide an electricmachine, wherein the winding is a moving winding or a stationarywinding.

It is another object of the invention to provide an electric conductoras disclosed herein wherein the electrically insulating coating isformed by a method comprising: contacting a bare wire with a bathcontaining an aqueous solution with a precursor for the electricallyinsulating coating, the bare wire providing the core; operating anelectrification device in electrical communication with the bare wire toelectrify the bare wire with a high voltage and a high current; andelectrochemically reacting the bare wire with the precursor in the bathto deposit the electrically insulating coating on an outer surface ofthe wire thereby producing the coated electric conductor. It is afurther object of the invention to provide an electrical conductorwherein the method of making the conductor further comprises:continuously feeding bare wire through a bath having a cathodicconnection and containing the aqueous solution comprising a precursorfor an electrically insulating coating; passing the electrified barewire through the aqueous solution comprising a precursor for anelectrically insulating coating in the presence of the cathodicconnection thereby passing current from the electrified bare corethrough said aqueous solution to the cathodic connection for a dwelltime sufficient to result in the electrochemically reacting of the wire;and continuously removing the coated electric conductor from the bath.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross section of an electrical conductor as a wireover-coated with an electrically insulating coating according to anembodiment;

FIG. 2 illustrates a cross section of an electrical conductor as a wireover-coated with an electrically insulating coating according to anotherembodiment;

FIG. 3 illustrates a schematic of an electric machine having anelectrical conductor as magnet wire in a coil;

FIG. 4 illustrates a schematic of a transformer having an electricalconductor as magnet wire in the primary and secondary coils;

FIG. 5 illustrates a schematic of a speaker having a voice coilcontaining the electrical conductor according to an embodiment;

FIG. 6 illustrates a wiring harness for an automobile containing anelectrical conductor according to an embodiment; and

FIG. 7 illustrates a schematic of process steps for coating an electricconductor according to an embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to compositions, embodiments andmethods of the present invention which constitute the best modes ofpracticing the invention presently known to the inventors. The Figuresare not necessarily to scale. However, it is to be understood that thedisclosed embodiments are merely exemplary of the invention that may beembodied in various and alternative forms. Therefore, specific detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for any aspect of the invention and/or as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention. It is also to be understood that thisinvention is not limited to the specific embodiments and methodsdescribed below, as specific components and/or conditions may, ofcourse, vary. Furthermore, the terminology used herein is used only forthe purpose of describing particular embodiments of the presentinvention and is not intended to be limiting in any way.

Except in the examples, or where otherwise expressly indicated, allnumerical quantities in this description indicating amounts of materialor conditions of reaction and/or use are to be understood as modified bythe word “about” in describing the broadest scope of the invention.Also, unless expressly stated to the contrary: percent, “parts of,” andratio values are by weight; the description of a group or class ofmaterials as suitable for a given purpose in connection with theinvention implies that mixtures of any two or more of the members of thegroup or class are equally suitable; description of constituents inchemical terms refers to the constituents at the time of addition to anycombination specified in the description, and does not necessarilypreclude chemical interactions among the constituents of a mixture oncemixed; the first definition of an acronym or other abbreviation appliesto all subsequent uses herein of the same abbreviation and appliesmutatis mutandis to normal grammatical variations of the initiallydefined abbreviation; and, unless expressly stated to the contrary,measurement of a property is determined by the same technique aspreviously or later referenced for the same property. It must also benoted that, as used in the specification and the appended claims, thesingular form “a,” “an,” and “the” comprise plural referents unless thecontext clearly indicates otherwise. For example, reference to acomponent in the singular is intended to comprise a plurality ofcomponents. Throughout this application, where publications arereferenced, the disclosures of these publications in their entiretiesare hereby incorporated by reference into this application to more fullydescribe the state of the art to which this invention pertains. The term“homogenous” as used herein refers to a layer which has the samecomposition throughout. In a refinement, the term refer& to a layer thathas the same composition on a size scale greater than 100 nm. Forexamples, a homogenous layer is not a layer having particles dispersedwithin a binder and in particular, a resinous binder. The term“insulating” as used herein refers to an electrical insulating property,measured as an electrical resistance.

FIG. 1 illustrates a cross section view of an electrical conductor 10according to an embodiment. The electrical conductor may be provided asa wire 12, and may have various cross sectional shapes, includingcircular as shown, rectangular, trapezoidal, and others as are known inthe art. The electrical conductor may be a single strand that is coatedwith a coating 14 having a plurality of pores 16, as shown. The pores 16define at least in part the increased surface area of coated wire asdescribed herein. Desirably, the wire 12 or other electrical conductormay be formed using aluminum or various aluminum alloys and the coating14 can be an electro-ceramic coating comprising metal oxides in additionto or instead of aluminum oxide.

In other embodiments, the electrical conductor may be a bundle of wires,such as multistranded wire or braided wire where individual strands areindividually coated or coated as a bundle. For a bundle of wires formingthe conductor, only some of the wires may be coated. In one variation,all of peripheral wires are coated with an electrically insulatingcoating, and in other variations, at least one of an interior wire isalso coated with the electrically insulating coating. In someapplications, all of the wires in the bundle are coated with theelectrically insulating coating.

Conventionally, electrical conductors, such as magnet wire and lowvoltage wire, are generally covered with an electrically insulatinglayer composed of organic material or enamel, and may require one tofour layers of polymer film and/or fiber insulation, often of twodifferent compositions, to provide an insulating layer. Even the mostrobust organic films are resistant to temperatures of only up to about240° C. The coating 14 according to the present disclosure providesimproved high temperature resistance such that coating 14 on magnet wireand low voltage wire has insulation that is resistant to temperatures ofgreater than 600° C. The coating 14 is chemically bonded to the aluminumwire such that the electrically insulating properties of the coating arenot destroyed with temperature cycling. Additionally, theelectrochemical coating 14 shows resilience to large temperature changesand thermal shocks without damaging the coating or losing its electricalinsulating properties. Wire coated with the electrochemical coating isalso protected from corrosion, which is beneficial for both unsealeduses of the electroceramic coating and for insulated wires having theelectroceramic coating as a first layer followed by other insulatinglayers. The electroceramic coating provides improved adhesion andsealing of the aluminum wire by the organic layers due to intimatecontact at the interface of the organic layers and electroceramiccoating due to increased surface area of the electroceramic coatingcompared to the bare aluminum wire surface area. The electroceramiccoating also acts as a barrier between the aluminum wire and anymoisture or condensation that penetrates an outer organic coating on thealuminum wire.

In one aspect of the disclosure, the aluminum or aluminum alloyconductor has an electrically insulating metal oxide coating layercomprising at least one non-aluminum metal oxide chemically bonded tothe conductor with no additional insulation or covering on the coatedwire. Desirably, the electrical application may operate at 120 volts orless and in applications approaching 640° C. when the coating on theconductor is otherwise unsealed. Magnet wire is one example of use ofsuch conductor. Magnet wire is used widely in numerous electricaldevices to change electrical energy to magnetic energy, and magneticenergy into electrical energy, for a variety of uses. Magnetic energycan be used to change or generate electrical energy; generate mechanicalmotion, e.g. sound or physical actuation; and the like. Suitableexamples using such wire include electrical motors; power tools, such asdrills; windings on transformers, e.g. step down transformers in cellphone chargers; electromagnets; inductors, e.g. for use in circuitboards; various types of sensors; variable differential transducers;solenoids; speakers; etc.

Alternatively, where extreme temperature resistance is not required, theelectroceramic coated wire may be used for higher voltage applications,that is greater than 120 Volts, provided that it is properly sealed orcoated with a material having insulating ability at such highervoltages. Numerous sealers and organic layers known in the art can beemployed to increase the breakdown resistance of the electroceramiccoated conductor such that higher voltage does not result in loss of theelectrical insulation of the conductor 10. Suitable uses for this aspectof the disclosure include conductors for use in corrosive environments,such as salt water, chemical plants, and are useful in automotive,marine, industrial and aerospace applications.

In another aspect of the disclosure, as shown in FIG. 2, oxide layer 14is the innermost base layer of electrical insulation on the conductor 10and is covered by one or more additional insulation layers 18 as areknown in the electrical arts, such as a conventional organic coating orenamel or shell as described above. Suitable examples of such wiring maybe for safety and sensor wiring. This may be particularly useful inautomotive applications to prevent short circuit of critical wiring, forexample for brake lights, tail lights, trailer lights and airbagapplications. If the outer conventional organic insulation 18 iscompromised through melting, burning, corroding, or the like by exposureto a hot spot, salt or other corrosive enviromnent, the inner basecoating layer of metal oxide prevents short circuiting of the conductor10.

Unlike commercially available organic coated wire products, theelectrical conductor 10 according to the present disclosure can sustainhigh operating temperatures without deterioration. The melting point ofpure aluminum is 660° C. and the electroceramic coatings do not melt andremain intact well above that temperature, such that heat degradation ofinsulation is reduced as a failure mode for coated wires according toFIG. 1. While most organic coatings, e.g. enameled products, begin todeteriorate at between about 90 to 240° C. and aluminum oxide anodizedfilms crack and craze at 300-450° C., the insulating coatings 14according to the present disclosure have been tested to temperatures ashigh as 620° C. and contacted with a heat source of 700° C. with novisible alteration in the appearance, and more importantly, whilemaintaining a high electrical resistance. This makes the conductorsparticularly useful in high temperature applications forelectromagnetically driven devices, such as solenoids, stators inelectric machines, coils, chokes and transformers.

Thermal cycling is an important measure of electrical device durability,particularly where the devices are subjected to intermittent use, suchas some electrical motors, adaptors and chargers for electronics and thelike. The inventive coatings are resistant to thermal cycling, across asmuch as about 800° C. of temperature differential, without electricalinsulation failure. That is, the conductor with a coating according tothe present disclosure does not experience any short circuiting of theconductor.

In another aspect of the invention, an article of manufacture comprisinga coil of magnet wire coated according to the disclosure is provided,the article can be selected from transformers, inductors, motors,speakers, hard disk head actuators, electromagnets, and other devicesincorporating electromagnetic coils or windings. Such articles providethe same power rating, e.g. motors and the like, with significantlyreduced motor weight and increased range of temperature performanceallowing higher temperature operation of, for example, solenoids andmotors without damaging the insulation which prevents device failure.Aluminum has less than ⅓ the density of copper and an aluminum conductorweights about ½ as much as a copper conductor of equal resistance andequal length. The weight reduction with only microns thick insulatingcoating is particularly useful in aerospace and automotive applicationswhere light weighting of products yields long term energy savings. Thelighter-weight aluminum conductor also provides superior performancecompared to copper in magnet wire used for moving windings, e.g.rotating windings and the like. The lower mass of aluminum results inlower inertia of the moving winding providing higher sensitivity andresponse in moving coils.

An electric machine may be an electric motor, an electric generator, oranother device using a magnetic coil. An electric machine may be anelectromechanical energy conversion device configured to changeelectricity into motion or motion into electricity. An electric machinemay also be a device that changes electricity, e.g. electrical energy,into a magnetic force. Examples of electric machines includetransducers, hard disk head actuators, solenoids, electric motors,electric generators, alternators, voice or speaker coils, and the like.In one example, an electric machine is illustrated in FIG. 3. Theelectric machine as illustrated is an electric motor and has a magnet22, a rotor 24 and a stator 26. The stator 26 is provided with coils 20of magnet wire. The electric motor may be any one of a number of typesof motors having a winding or coil including: direct current (DC),alternating current (AC), self-commutated, externally commutated,brushless, asynchronous, synchronous, and the like. In another example,the rotor is provided with the coils. The coil 20 may be provided as afield winding and/or an armature winding. The magnet wire in the coils20 may be the coated electrical conductor according to the presentdisclosure and as illustrated and described with respect to FIG. 1 orFIG. 2.

In another example, another electric machine is illustrated in FIG. 4.The electric machine transforms electricity into a magnetic force, andpossibly back into electricity. Examples of electric machine devicesinclude transformers, inductors, electromagnets, and the like. Theelectric machine as illustrated is a transformer 31 with a magnetic core32, a primary coil 34 and a secondary coil 36. Both coils 34 and 36 areprovided with magnet wire 30. V1 and V2 represent two different voltagesresulting from transformation of a voltage in one coil into a differentvoltage in the other coil. The magnet wire 30 may be the coatedelectrical conductor according to the present disclosure and asillustrated and described with respect to FIG. 1 or FIG. 2.

In yet another embodiment, a voice coil actuator is illustrated in FIG.5. A voice coil actuator may be used in a speaker, transducer, and otherapplications. The voice coil actuator as illustrated is a speaker 41with a voice coil 40, a magnet 42, signal inputs 44, diaphragm 46 andframe 48. When an electrical signal is applied to the voice coil, themagnet and coil interact, generating a mechanical force that causes thediaphragm 46 to move back and forth, thereby producing sound. The voicecoil 40 is provided with magnet wire. The magnet wire in the coil 40 maybe the coated electrical conductor according to the present disclosureand as illustrated and described with respect to FIG. 1 or 2.

In a further embodiment, a solenoid is provided with a magnet wire coilwith the electrical conductor as described and illustrated with respectto FIG. 1. Examples of solenoids with magnet wire include valves, doorlocking mechanisms, and the like. Normally closed solenoids that need toremain open for long periods of time show improved durability andcontinue to work without failure because of the drastically enhanceddurability of the insulation coating of the disclosure.

In another embodiment, a wiring harness is illustrated in FIG. 6. Thewiring harness may be used to transmit signals and/or electrical powerbetween components. The wiring harness may be used in a variety ofapplications, and includes automotive, aerospace, marine, consumerproducts, and others. The wiring harness illustrated has a bundle ofwires with various connectors on each end. Each wire 50 of the harnessmay be an electrical conductor as described and illustrated with respectto FIG. 1. In another example, each wire 50 of the harness may be anelectrical connector as described and illustrated with respect to FIG.2.

In one aspect, the initial insulating properties, i.e. electricalresistance to conductance through the insulating coating, and insulatingproperties after high temperature exposure remain significantly higherthan fresh copper magnet wire. In another aspect, aluminum conductorcoated according to the invention has lower stray current lossescompared to copper, which is an improvement over conventional productsand is less expensive than copper.

In a refinement, insulating coating 14 comprises at least 10 weightpercent aluminum oxide of the total weight of the insulating coating andat least one metal oxide that is not aluminum oxide. In anotherrefinement, insulating electro-ceramic coating 14 may include aluminumoxide in an amount of at least, 5, 10, 15, 20, 25, or 30 weight percentof the total weight of the coating and independently may includealuminum oxide in an amount of at most, 80, 75, 70, 60, 50, or 40 weightpercent of the total weight of the coating.

In some embodiments, the metal oxide or oxides other than aluminum oxideare present in an amount of at least 10, 15, 20, 25, 30, 35, 40, 45, or50 weight percent of the total weight of the insulating coating and atmost 95, 90, 85, 80, 75, 70, 65, 60, 55 weight percent of the totalweight of the coating.

The electrically insulating electro-ceramic coating 14 is directly,chemically bonded to the conductor or wire substrate surface and has aninterface with the metal surface. Inclusion of aluminum, at leastpartially from the metal surface into the electro-ceramic coating 14provides improved adhesion of the coating. In a variation, the aluminumoxide concentration varies over the thickness of the insulatingelectro-ceramic coating, wherein amount of aluminum oxide is greater atthe coating substrate interface and generally decreases with increasingdistances away from the wire substrate metal surface. For example, thealuminum concentration may be 10 to 50 percent greater at 0.1 micronsfrom the interface than at 3, 5, 7, or 10 microns from the interface.

In one example, the metal oxide other than aluminum oxide includestitanium dioxide. Examples of suitable metal oxides other than aluminumoxide include, but are not limited to, oxide coatings that includetitanium oxide, zirconium oxide, hafnium oxide, tin oxide, germaniumoxide, boron oxide, iron oxides, copper oxides, manganese oxides, cobaltoxides, cerium oxides, molybdenum oxides, tungsten oxides, yttriumoxides, bismuth oxides, zinc oxide, vanadium oxides, or combinationsthereof. The oxide coating can advantageously be a homogenouselectro-ceramic layer prepared as set forth below in more detail. Theinsulating coating 14 may include the aluminum oxide and the metal oxideor oxides other than aluminum oxide in combination in homogeneous formsuch that the insulating electro-ceramic coating can be the samethroughout. Alternatively, coating 14 may include the aluminum oxide andthe other metal oxide combination in a form having domains (e.g., grainsor crystallites) of the aluminum oxide and domains of the metal oxide oroxides other than aluminum oxide. The electro-ceramic coating 14 mayhave amorphous and crystalline regions. This variation does not includea binder resin or matrix to hold the oxide mixture. The coating 14 doesnot include sintered monoliths, casements or ceramic bodies or loos orcompressed powdered oxides, but instead is a coating chemically bondedto the aluminum or aluminum alloy wire.

In a refinement, coating 14 may be in direct contact with the underlyingbare aluminum or aluminum alloy wire and can be also exposed toenvironment. The coating 14 provides an electrically insulating coatingfor the bare wire 12, and has a higher resistivity than the bare wires12, such as aluminum. By coating the wire 12 in the conductor 10, thewire is electrically insulated, to prevent the wire from shorting, etc.during use.

In one example, the coating is provided with titanium dioxide. Theelectrically insulating coating 14 may have an electrical resistance of1, 2, 3, 4, 5, 6, 7, 10, 15, 20, or 30 Megaohms. In another example, theelectrically insulating coating 14 may have an electrical resistance of3, 4, 5, 6, 7, 10, 15, 20, or 30 Megaohms per centimeter. In oneexample, the coating 14 may have an electrical resistance of 10, 15, 20,25, or 30 Megaohms after the coating process and before the electricalconductor is used in an application. In another example, the coating 14may have an electrical resistance of 10, 15, 20, 25, or 30 Megaohms percentimeter after the coating process and before the electrical conductoris used in an application.

Titanium dioxide is a semiconductor material with a relatively high bandgap. Electroceramic coatings containing titanium dioxide and aluminumoxide as disclosed herein were tested for dielectric strength using a GWInstek Model GPT 815, dielectric breakdown testing device, according toASTM D149-09 (2013) test specification. Measurements indicate that thecoatings 14 had a dielectric strength of 180-300 Volts at 10micrometers, as measured ASTM D149-09 (2013). As such, the coating 14may be used as the sole electrical insulator for the conductor 10 inapplications ranging from fractions of a Volt up to and including 120Volts. When an application uses a voltage above the dielectric strengthof the material, the material may allow leakage of current. A benefit oftitanium dioxide coating on aluminum wire as compared to organic, e.g.plastic, insulation is that short term voltage surges above 120 voltsmay allow leakage, without permanent damage to the insulating ability ofthe coating at lesser voltages. In contrast, a short circuit of anorganic coated wire irreversibly damages the insulation, creating apermanent arc spot or short in the wire.

Additionally, the coating 14 as described herein may be heatedrepeatedly up to approximately 600, 610, 620, 630 or 640° C., or nearthe melting temperature of the underlying wire 12 while maintaining theelectrical resistance of the coating, as shown below in the examples.This makes the coating 14 useful in high temperature applications thatwould otherwise be unavailable for a conventional insulating coating.

The insulating coating 14 typically increases wire surface area comparedto bare wire surface area. The increased surface area provides forincreased radiative emission from the wire, as well as improvedconvective cooling. This may aid in thermal management of the electricalconductor 10 or the device itself in various high temperatureapplications or devices. In this regard, the coating 14 may have asurface area from 10 and 1000 times greater than the surface area of abare wire (e.g. aluminum or aluminum alloy) before being coated with thecoating. In a refinement, the coating 14 may have a surface area atleast 100 times greater than the surface area of a bare wire beforebeing coated with the insulating coating. In another refinement, thecoating 14 may have a surface area approximately 700 times greater thanthe surface area of a bare wire before being coated with the insulatingcoating. The surface area can be determined by the BET method which isset forth for example by ASTM C1274-12; the entire disclosure of whichis hereby incorporated by reference. In other refinements, the coating14 typically has a surface area that is about 10, 20, 30, 40, 50, 60,70, 80, 90, 100, 120, 130, 140, 150, 170, 180, 190, 200 times greaterthan the surface area of the underlying coated wire, e.g. than that of abare wire. In a further refinement, the coating 14 has a surface areabetween 100 to 1000 times greater than the surface area of theunderlying coated wire, e.g. than that of a bare wire. In yet otherrefinements, the coating 14 typically has a surface area less than 1000,500, 400, 350, 300, 250, or 225 times greater than the surface area ofthe underlying coated wire, e.g. than that of a bare wire. In general, awire having electro-ceramic coating deposited thereon may have a surfacearea that is about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 130,140, 150, 170, or 200 times greater than the surface area of theunderlying coated wire and less than 1000, 950, 900, 850, 800, 750, 700,650, 600, 550, 500, 450, 400, 350, 300, 250, 225 times greater than thesurface area of the underlying coated wire. According to one example,coating 14 increases the surface area of a wire by one to two orders ofmagnitude, i.e. ten times or one hundred times, or the like. In afurther example, the BET surface area of the coating can be 140-700times the BET surface area of the bare metal wire, and has a weight of800 mg per square foot. In another example, the surface area of theinsulating coating 14 can be in the range of 100-1000 times the crosssectional area, and in a further example is 700 times the crosssectional area.

The insulating electro-ceramic coatings are typically stable inultraviolet (UV) light. Additionally, the coatings 14 may be scratchresistant, and may be able to bend with the wire 12 or the coated wireswithout delaminating, cracking or breaking. The coatings 14 aresufficiently thin such that they do not significantly increase theoverall weight of the electrical conductor. In one example, theinsulating coatings are generally at least about 1, 3, 5, 7, 9, 10, 11,or 12 microns in thickness, and are generally not more than about 25,20, 28, 16, 15, 14, or 13 microns in thickness. In a further example,the insulating coatings are between 0.5 to 50 microns in thickness. Insome examples, the insulating coatings increase the mass of thesubstrate from 4 to 20 g/m², depending on thickness and chemicalcomposition.

The coating 14 may be typically a uniform coating having a constant orgenerally constant thickness about the perimeter of the wire 12.Desirably, this uniformity is achieved in the absence of a polishing,grinding or other removal of coating. In one embodiment, thickness mayvary by 0 to 25%, for example at least 1, 3, 5, 7, 9 or 10%, anddesirably no more than 25, 20, 18, 16, 14, or 12%, with highertolerances being acceptable with thicker coatings. The electricallyinsulating electro-ceramic coating provides for electrical insulation ofthe bare wire 12. The coating 14 on the wire has been demonstrated topass a T-bend test of 0T-1T showing a high bend strength and highadhesion to the wire to provide flexibility under weathering conditionsand subjected forces during use.

The coating 14 may have a plurality of pores 16. These pores 16 defineat least in part the increased surface area of coated wire as set forthabove. The pores 16 may also provide a surface for improved chemical andmechanical adhesion of any additional coatings or shells on theconductor 10, such as an organic insulating layer or an additional highvoltage sealer.

As set forth above, the wire 12 includes a high surface area, highlyelectrically resistive coating disposed over its surface. In particular,these coatings may be prepared by the processes set forth in U.S. Pat.Nos. 6,797,147; 6,916,414 and 7,578,921; the entire disclosures of whichare hereby incorporated by reference. In general, the coatings areformed by a method in which a bare wire can be contacted with a bathcontaining an aqueous solution with a precursor for the electro-ceramiccoating. The bare wire is electrified with a high voltage and a highcurrent; and electrochemically reacts with the precursor in the bath toprovide the electrically insulating coating on an outer surface of thewire. As used herein “high voltage” used in the coating apparatus andprocess includes peak voltage potential of at least about 140 volts upto about 800 volts; “high current” as used herein includes effectivecurrent of at least about 20 amps and up to about 1000 amps per wire.These values may be varied while practicing the continuous coatingprocess within power applied ranges of at least 10, 20, 30, 40 or 50 kWper wire. Greater kW may be applied to a wire provided the wire hasgreat enough cross-sectional area to withstand the added kW withoutdamage to the wire.

Direct current and/or alternating current can be used. In someembodiments, the current may be a square wave form pattern with afrequency of approximately 0.01-40 milliseconds. Frequency may beadjusted from 25 Hz to 25,000 Hz, may be high frequency such as200-25,000 Hz or 100-10,000 Hz. Waveforms may include sinusoidal,triangular, and/or rectangular in any of AC, DC or pulsed DC current, aswell as complex waveforms containing superimposed waveforms, e.g. an ACwaveform over a DC waveform.

High current is an effective current at or greater than about 20-1000Amps per wire. As wire size increases so does current carryingcapability without damage to the wire. During electrolytic coating, toomuch current through a wire may result in excessive heating of the wire,resulting in embrittlement of the wire. Depending upon the gage of wireto be coated the amperage may be adjusted to at least 20, 30, 40, 50,60, 70, 80, 90, or 100 Amps and preferably not more than 1000, 800, 600,400, 300, 200 180, 160, 140, 120 Amps per wire, i.e. a single strand ofwire, for high tension wire. Applied current may be alternating current,asymmetric alternating current, direct current, or pulsed directcurrent. In some examples, direct current is used and may be applied asan on/off waveform. In one embodiment, a total period of the waveform isat least 0.01, 0.1, 1 or 10 milliseconds and up to 50, 40, 30, 20 or 15milliseconds. Waveforms may be adjusted to a ratio of at least: 0.1,0.3, 0.6, 1.0, 1.2, 1.5, 1.7, 2.0, 2.2, 2.5, 2.8, 3.0, 5.0, 10.0, or upto an infinite ratio where the direct current is always on and there isno off portion, also referred to as straight DC.

Generally, residence time ranges from about 1, 2, 3, 4, 5, 6, 8, or 10seconds and at least for efficiency is not more than 180, 160, 140, 120,100, 60, 45, 30, 20 or 15 seconds. In one example, the residence time isapproximately five to ten seconds. Generally, feed rate or wire speed isdependent upon achieving sufficient residence time for desired coatingproperties, e.g. thickness, surface area and resistivity, and desirablycan range from about 10 feet per minute to about 200 feet per minute.Higher speeds may be used provided that residence time is maintained.

In another embodiment, the resistivity of the coating is modified bychanges in the identity of the electroceramic coating precursors in theelectrolytic bath, e.g. precursor elements may include Ti, Zr, Zn, Hf,Sn, B, Al, Ge, Fe, Cu, Ce, Y, Bi, P, V, Nb, Mo, Mn, W and Co. In oneembodiment, features of the coating are adjusted by changing aluminumand/or zirconium concentration of the aqueous solution. The inclusion ofaluminum oxide and/or zirconium oxide advantageously allows theadjustment of coating features, e.g. the abrasion resistance of theinsulating coating. The chemical precursors used for forming theelectrically insulating coating are preferably free of the followingchemicals: chromium, cyanide, nitrite ions, oxalates; carbonates;silicon, e.g. siloxanes, organosiloxanes, silanes, silicate;hydroxylamines, sodium and sulfur. Specifically, it is increasinglypreferred in the order given, independently for each preferablyminimized component listed below, that precursor for the electro-ceramiccoating according to the invention, when directly contacted with metalin a process according to this invention, contain no more than 1.0,0.35, 0.10, 0.08, 0.04, 0.02, 0.01, 0.001, or 0.0002 percent of each ofthe following constituents: chromium, cyanide, nitrite ions; oxalates;carbonates; silicon, e.g. siloxanes, organosiloxanes, silanes, silicate;hydroxylamines, sodium and sulfur.

The aluminum or aluminum alloy wire used in the conductor 10 may becontinuously coated with an electro-ceramic stable coating. The coatingmay be applied during a continuous process. In one example, thecontinuous process is provided as illustrated in FIG. 7.

In FIG. 7, in step 60, metal is formed into wire; this is an optionalstep in the process. Starting with a metal workpiece, an extrusionprocess, drawing process, or other metal-forming process may be used togenerate a bare wire using aluminum or an aluminum alloy. Alternatively,step 60 may comprise obtaining commercially available bare aluminum wireof desired geometry and providing same to the coating line.

In processes according to the invention, bare wire may be provided on aspool, reel or other wire carrier, which may be used to feed wire intothe coating process. Desirably, the wire carrier for feeding the barewire into the coating process comprises a spool, reel or the like aboutwhich the bare wire is wound. Bare wire will be understood by those ofskill in the art to mean wire having surfaces of metallic aluminum or analuminum alloy in the absence of a durable applied coating or sheathing,such as paint, insulation, conversion coatings and the like; bare wiremay include some contaminants such as forming lubes, oils, soils and athin alumina layer formed by environmental oxidation, as well astemporary treatments applied for transport to reduce damage to wiresurfaces. In one non-limiting example, wires may have various diametersas is known in the art for electrical conductors for use with electricalpower applications up to approximately 120 Volts.

In one embodiment, the bare wire is coated using a coating sub-processfor a wire, shown collectively as block 62. Processes according to theinvention may include a greater or fewer number of steps, differentvariations of a step, and various steps in the process may also beordered differently from the illustrated flow chart in otherembodiments. For example, bare wire having only minor amounts ofcontaminants on the wire surfaces, may be coated in the absence of apre-cleaning step or heavily contaminated wires may benefit from apre-clean step with several sub-steps such as cleaning, pickling andrinsing.

In FIG. 7, at step 64, spool A containing bare wire is connected to,e.g. placed in, or on, a coating apparatus. The bare wire end is fedthrough the coating apparatus and connected to a spool B. Spool B isdesignated as a spool having coated wire thereon. A short section ofwire on spool B may be uncoated based on the initial setup of theapparatus before operation, e.g. connection of the bare wire end toSpool B provides a short initial length of uncoated wire on Spool B. Inother embodiments, the bare wire is fed directly into the coatingapparatus from another process, such as a metal forming or other metaltreatment process, and there is no feed spool, e.g. spool A, provided.Likewise, the coated wire may be directly fed into other processingstations after coating instead of onto a collecting spool, such as anadditional coating step for an enamel or organic shell or coating. Theforegoing integrated processes may be used provided that the currentrunning through the coating solution and the electrified wire does notinterfere with other operations and is not unfavorable from an economicor health and safety view.

At step 66, the wire in the apparatus is electrified to a high currentand a high voltage, as described herein, using an electrification devicesuch that the wire acts as an anode within the bath of a solutioncontaining chemical precursors for the coating. In one example, theelectrification device is a rotary switch having a contact wheel thatrotates with passage of the wire as the wire is fed through the process,and the device may include a liquid mercury rotary contact. A cathode isprovided within the bath. Both the electrification device and thecathode are electrically connected to a power source, which whenactivated passes current to the wire via the electrification device, theelectrical current passing from the anodic wire through solution to thecathode.

At step 68, a motor is operated to feed wire through the bath to coatthe wire. The type of motor to be used is not particularly limited inany way, and can include for example an electric motor, an internalcombustion engine, motors based on pneumatic or hydraulic power or thelike. If only for economy, an electric motor is preferred. In oneembodiment, speed of the wire is adjustable based on a feedback loopproviding data on coating features, such as coating thickness measured,for example in real time or otherwise to a controller. In oneembodiment, a user interface is provided for monitoring wire speed,motor parameters and allows making changes to same with adjustment and /or other devices associated with the apparatus.

At step 70, a cleaning device, such as a spray system, an acid oralkaline cleaning bath, ultrasound device, deoxidizing bath and/or anair knife, may be operated to clean the bare wire before it enters thesolution in the coating bath. In one example, a spray system provideshigh pressure deionized water to clean the wire. The cleaning processcan provide a better and more uniform substrate surface for coatingdeposition, and may also reduce introduction of debris or othercontaminants into the coating bath.

At step 72, the wire proceeding through the bath is coated via anelectrochemical process thereby providing a ceramic coating on thesurface of the wire. In one embodiment, the solution in the bath is anaqueous solution containing a coating precursor comprising a source oftitanium and a source of phosphorus. In one example, the aqueoussolution contains H₂TiF₆ and a source of phosphorus. An electro-ceramiccoating is deposited on the wire surface which comprises oxides ofmetals from the substrate and from the solution. In one embodiment, anoxide coating, which comprises aluminum oxide and titanium dioxide, isformed on the surface of the aluminum wire. Desirably, aluminum oxide ispresent in the coating in amounts of 1-25 wt. %, with the remaindercomprising titanium dioxide and non-zero, small amounts of elements fromthe bath. In one example, the coating includes aluminum oxide in anamount of at least, 5, 10, 15, 20, or 25, or 30 weight percent of thetotal weight of the insulating coating. In another refinement,electro-ceramic coating includes aluminum oxide in an amount of at most,80, 75, 70, 60, or 50, or 40 weight percent of the total weight of theinsulating coating. Typically, the metal oxide or oxides other thanaluminum oxide are present in an amount of at least 20 10, 15, 20, 25,30, 35, 40, 45, or 50 weight percent of the total weight of theinsulating coating. In a variation, the aluminum oxide concentrationvaries over the thickness of the insulating coating being greater at thecoating substrate interface and generally decreasing as with increasingdistances away from the wire substrate. For example, the aluminumconcentration may be 10 to 50 percent higher at 0.1 microns from theinterface than at 3, 5, 7, or 10 microns from the interface.

In another embodiment, the resistivity of the coating is modified bychanges in the identity of the electroceramic coating precursors in theelectrolytic bath, e.g. precursor elements may include Ti, Zr, Zn, Hf,Sn, B, Al, Ge, Fe, Cu, Ce, Y, Bi, P, V, Nb, Mo, Mn, W and Co. In oneembodiment, features of the coating are adjusted by changing aluminumand/or zirconium concentration of the aqueous solution. The inclusion ofaluminum oxide and/or zirconium oxide advantageously allows theadjustment of coating features, e.g. the color and/or abrasionresistance of the insulating coating.

A visible glow or visible light discharge may occur along the surface ofthe wire as the coating is being formed. The electrochemical process maybe a plasma process. The wire may provide an anode connection withoxygen radicals reacting with titanium anions at the surface of the wireto form a titanium oxide, such as titania. Protons at the cathodeconnection in the bath may lead to formation of hydrogen gas as water inthe aqueous solution is electrolyzed, which desirably may be controlledand removed by one or more optional hoods or venting systems. In otherexamples, other chemical solutions may be used to provide a coated wire.

At step 74, a control system including a controller is used to controlthe speed of the motor, and the speed of the wire. By changing the speedof the wire, the residence time of the wire in the bath may becontrolled, thereby together with other process parameters, controllingthe thickness of the coating and the amount of dissolution of aluminumfrom the wire. Longer residence times for the wire may also be obtainedby for example, defining a longer path through the bath. The thicknessof the coating may also be controlled by modifying the wave form and/orvoltage utilized. The control system is also useful in adjusting spoolspeed for spools A and B. For wire provided on a spool, to maintain aconstant speed of wire travel through the bath as the wire is taken offof spool A, the rotational speed of spool A may be increased tocompensate for the smaller amount of wire provided by each rotation.Likewise, as the coated wire accumulates on spool B, to maintain thesame feed velocity of the wire, the rotational speed of spool B may bedecreased to compensate for the greater amount of wire accumulatedduring each rotation around the increasing circumference of spool B dueto added coated wire. An accumulator, which may store up to perhaps 300meters or more of wire ahead of the main section of the processing line,may be utilized to control wire speed and contact time in the bath. Thecontrol system may also control a cooling system connected to the bathto cool the solution and maintain the solution temperature within apredetermined range, desirably from ambient temperature, generally about20° C. to less than 100, 95, 90, 80, 70, 60, 50 or 40° C.

At step 76, after the wire leaves the bath any excess solution remainingon the coated wire may be removed and desirably the coated wire may berinsed with water. In one embodiment, the excess solution, with orwithout rinse water can be returned to the bath in a recycling process.At step 78, the coated wire is collected onto spool B. When spool A isempty or near empty, the coating process 62 is stopped and spool Bcontaining coated wire is removed from the apparatus.

Although the coating process 62 is described for a single wire, multiplewires may be fed through the bath simultaneously, with each wire beingelectrified at a high power, as described herein. For simultaneouslycoating multiple wires, a minimum separation between the electrifiedwires should be maintained to avoid arcing and each wire may be providedwith separate electrification devices and guides as well as suppliedfrom and collected on separate spools.

The following examples illustrate the various embodiments of the presentinvention. Those skilled in the art will recognize many variations thatare within the spirit of the present invention and scope of the claims.

EXAMPLES Example 1

An aluminum wire was immersed in an electrolyte comprising dissolved Ti,phosphate and an etchant. The aluminum wire was 0.76 mm in diameter andhad a residence time in the bath of 10 seconds at 490 Volts (PeakVoltage) and 185 Amps. The wire was removed from the electrolyte bathand coating thickness and content was measured. About 10 microns oftitania-containing electroceramic coating was present.

The titania coated wire was tested against two commercially availablebenchmark copper wires conventionally coated with an insulating coatingby the manufacturer. Copper Wire Benchmark 1 was a copper magnet wire0.74 mm in diameter coated with an organic insulating coating. The wirewas removed from a wire coil of an electrical drill motor from an 18 Vcordless Craftsman brand drill commercially available from Sears. CopperWire Benchmark 2 was a commercially available copper magnet wire 0.66 mmin diameter coated with an organic insulating coating. The wire iscommercially available from EIS Wire and Cable, and the organicinsulating coating on the wire was reported by the manufacturer as beingpolyester (amide) (imide) overcoated with polyamideimide, Thermal class200C. All three samples were tested for initial electrical insulationperformance of their coatings, see starting resistance below. Theresistance in all samples was measured between the outer surface of thecoating and a core region of the sample; for samples where the coatinghad been removed, the measurement was taken from the outer surface ofthe wire.

In Test A, a first set of samples was heated to 450° C. for a residencetime of eight hours, cooled to ambient temperature and their resistancewas measured.

A second set of samples was subjected to Test B, where all samples wereheated to 620° C. for a residence time of one hour, cooled to ambienttemperature and their resistance was measured.

TABLE 1 Resistance Initial Resistance after after Conductor resistanceTest A Test B Comparative Example 1A: 6.0 <0.1 ohms, Insulation CopperWire Benchmark 1 Megaohms Insulation burnt failed at Wire diameter =0.74 mm off by test. 450° C. Comparative Example 1B: 6.0 <0.1 ohms,Insulation Copper Wire Benchmark 2 Megaohms Insulation burnt failed atWire diameter = 0.66 mm off by test. 450° C. Example 1: 20 7.0 Megaohms7.0 Titania Coated Al Megaohms Megaohms Wire diameter = 0.76 mm

The above results show that the bare titania coated aluminum electricalconductor of Example 1 maintained insulating ability of 7 Megaohms afterexposure to high temperatures of 450 to 620° C. In contrast, the organiccoatings of Comparative Example 1A, and even Comparative Example 1Butilizing polyamideimide, lost their insulating features when exposed tothese high temperatures.

Example 2

Insulation testing and hot spot testing were performed on electricalconductors having a coating according to the present disclosure with asecond insulating organic layer applied to the outer surface of theelectroceramic coating and on commercially available electricalconductor having an insulating organic layer applied by the wiremanufacturer.

An aluminum wire was immersed in an electrolyte comprising dissolved Ti,phosphate and an etchant. The aluminum wire was 0.76 mm in diameter hada residence time in the bath of 10 seconds at 410 Volts (Peak voltage).The wire was removed from the electrolyte bath and coating thickness andcontent was measured. About 10 microns of titania-containingelectroceramic coating was present on the aluminum conductor wire. Anadditional outer insulating organic sheath with 0.36 mm thickness wasprovided on the outer surface of the titania containing coating. Theouter insulating organic sheath was Ethylene ChloroTriFluoroEthylene(ECTFE fluoro polymer), commercially available from Solvay SpecialtyPolymers USA, LLC under the brand name Halar®.

The titania coated wire was tested against a commercially availablebenchmark copper wire conductor taken from a standard automotive trailerhitch wiring harness. The conductor had an overall diameter of 2.4 mmand contained a multistranded copper wire bundle measuring 1.024 mm (18gage). The copper wire bundle was covered with a thick conventionalinsulating layer having a calculated thickness being approximately 0.69mm.

The electrical resistance was measured between the outer surface of thesample, and a core region of the sample. All samples were tested forinitial insulation performance of their coatings, see Initial Resistancebelow. All samples were laid on a hot plate for a time sufficient toremove portions of the outer organic insulating layer, cooled to ambienttemperature and their resistance was measured. The hot plate had atemperature of 700° C., but did not melt the aluminum wire, due to theshort time taken to destroy the insulation, and possible due to the highsurface area of the electroceramic coating on the aluminum wire.

TABLE 2 After melting off standard insulation Conductor InitialResistance on a hot plate Comparative Example 2: Copper 24 Megaohms 0.1ohms Wire Benchmark 3 Example 2: >30 Megaohms 4 Megaohms Aluminum wirehaving an inner (above testing (even in charred coating layer containingtitania equipment range) insulation areas and and an outer layer of anorganic areas free of the insulation. organic insulation)

The above results show that aluminum electrical conductors coated withan outer layer of organic coating, and with an inner titania containinginsulating layer of Example 2 had initial insulating performance (>30Megaohms) of more than 20% higher than the conventional organicinsulation of Comparative Example 2 (24 Megaohms). The above resultsalso show that the titania coated aluminum electrical conductor ofExample 2 maintained insulating ability of 4 Megaohms after charring anddestruction of the organic insulating outer layer. In contrast, theorganic coatings of Comparative Example 2, lost their insulatingfeatures and where destroyed when exposed to these high temperatures.

Example 3

A thermal shock test was performed on samples of coated aluminum alloyconductor according to the present disclosure having a metal oxidecoating comprising titanium dioxide and aluminum oxide, and on samplesof a conventional anodized aluminum alloy conductor. The conventionalanodized aluminum alloy conductors were anodized in a Class 1 sulfuricacid anodizing process, and the resulting oxidation layers were about 18microns in thickness on samples of Comparative Example 3.

Samples of aluminum alloy wire were immersed in an electrolytecomprising dissolved Ti, phosphate and an etchant. The aluminum alloywire samples were 0.76 mm in diameter had a residence time in the bathof 10 seconds at 410 Volts (Peak voltage). The aluminum alloy wiresamples were removed from the electrolyte bath and coating thickness andcontent was measured. About 10 microns of titania-containingelectroceramic coating was present on the aluminum alloy wire samples ofExample 3.

Initial electrical resistance of each of the coated aluminum alloysamples was measured and the appearance was noted. The coated aluminumalloy samples were placed in an oven at 600° C. for one hour, reaching apeak metal temperature of 600° C., and then directly transferred intoliquid nitrogen at −197° C. for 5 minutes. The samples were removed fromthe liquid nitrogen and allowed to warm to ambient or room temperature.The resistance was re-measured and the appearance was noted.

TABLE 3 Resistance after ΔT Initial Appearance Appearance of 797° C.electrical before after thermal thermal Coating resistance thermal shockshock shock test Example 3: 20 Grey Blue No visible 7 Megaohms TitaniaMegaohms change coated Al Comparative 23 Clear/silver Dark brown, 3-20ohms Example 3: Megaohms significant (0.000003 to Anodized Aldelamination 0.000020 and spalling Megaohms)

The above results show that the bare titania coated aluminum alloyelectrical conductors of Example 3 showed some reduction in resistance,but maintained insulating ability of 7 Megaohms after exposure to hightemperature of 600° C., and sudden thermal shock caused by a AT of 797°C. In contrast, the anodized aluminum alloy electrical conductors ofComparative Example 3, while having an initially acceptable insulatingability, lost substantially all insulating ability when exposed to thethermal shock test, retaining less than 1×10⁻⁵ of the resistance ofExample 3's coating. Comparative Example 3 also showed delamination andspalling of the alumina coating.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. An electrical conductor comprising: anelectrically conductive core having an outer surface, the corecomprising aluminum; and an electrically insulating coating chemicallybonded directly on the outer surface of the core, the coating comprisingat least one non-aluminum metal oxide, the coating being electricallyresistant at high temperatures.
 2. The electrical conductor of claim 1wherein the electrical conductor maintains an electrical resistance atambient temperature after heating to at least 450° C.
 3. The electricalconductor of claim 1 wherein the electrical conductor maintains anelectrical resistance of at least 1 Megaohm at ambient temperature afterthermal cycling to at least 600° C.
 4. The electrical conductor of claim1 wherein the core further comprises an aluminum alloy.
 5. Theelectrical conductor of claim 1 wherein the at least one non-aluminummetal oxide comprises titanium dioxide and the conductor is an aluminumor aluminum alloy conductor.
 6. The electrical conductor of claim 1wherein the electrically insulating coating has an electrical resistanceat ambient temperature before the electrical conductor is used of 3 to30 Megaohms.
 7. The electrical conductor of claim 1 wherein the coatingis the sole electrical insulator for the electrical conductor and thecoating is electrically insulating at applied voltages of up to 120volts and peak voltage of up to about 140 volts.
 8. The electricalconductor of claim 1 wherein the coating has a resistance of at least 4Megaohms at ambient temperature after exposure to a temperature greaterthan 250° C., preferably greater than 300° C.
 9. The electricalconductor of claim 1 wherein the coating has a thickness being in arange of 0.5 to 50 microns.
 10. The electrical conductor of claim 1wherein the electrically insulating coating is homogenous.
 11. Theelectrical conductor of claim 5 wherein the electrically insulatingcoating further comprises aluminum oxide and has an interface with theouter surface of the core; and wherein aluminum oxide concentration isgreater at the interface with the outer surface of the core anddecreases with increasing distance away from the interface.
 12. Theelectrical conductor of claim 1 wherein the electrically insultingcoating has a surface area of at least 100 times greater than thesurface area of the bare core prior to being coated with theelectrically insulating coating.
 13. The electrical conductor of claim 1wherein the electrically insulating coating is an electro-ceramiccoating.
 14. The electrical conductor of claim 1 further comprising anelectrically insulating shell surrounding the coating, such that thecoating is positioned between the shell and the core.
 15. The electricalconductor of claim 14 wherein the electrically insulating shellcomprises an enamel, a sealant, an organic coating.
 16. A wire harnessfor transmitting at least one of signals and electrical power, the wireharness comprising: at least one wire formed from the electricalconductor according to claim
 1. 17. The wire harness of claim 16,wherein the at least one wire formed from the electrical conductor ispart of a 120 volts or less circuit.
 18. An electric machine comprising:a winding comprising the electrical conductor according to claim
 1. 19.The electric machine of claim 18, wherein the winding is a movingwinding.
 20. The electric conductor of claim 1 wherein the electricallyinsulating coating is formed by a method comprising: contacting a barewire with a bath containing an aqueous solution with a precursor for theelectrically insulating coating, the bare wire providing the core;operating an electrification device in electrical communication with thebare wire to electrify the bare wire with a high voltage and a highcurrent; and electrochemically reacting the bare wire with the precursorin the bath to deposit the electrically insulating coating on an outersurface of the wire thereby producing the coated electric conductor. 21.The electrical conductor of claim 20 wherein the method furthercomprises: continuously feeding bare wire through a bath having acathodic connection and containing the aqueous solution comprising aprecursor for an electrically insulating coating; passing theelectrified bare wire through the aqueous solution comprising aprecursor for an electrically insulating coating in the presence of thecathodic connection thereby passing current from the electrified barecore through said aqueous solution to the cathodic connection for adwell time sufficient to result in the electrochemically reacting of thewire; and continuously removing the coated electric conductor from thebath.